1. Field of the Invention
This invention relates to a compound type microscope comprising a combination of a scanning tunnel type microscope (STM), an atomic force microscope (AFM) and an optical microscope.
2. Related Background Art
In recent years, there have been actively developed scanning tunnel type microscopes and atomic force microscopes in which a probe is brought close to the surface of a sample and scans the latter and a tunnel current or an atomic force acting between the probe and the sample is detected to thereby observe the minute structure of the surface of the sample.
The principle of the operation of the atomic force microscope (hereinafter referred to as the AFM) will hereinafter be described briefly with reference to FIG. 12 of the accompanying drawings. Light emitted from a light source 71 is condensed by a collimator lens 72, forms a spot on the reflecting surface of a cantilever 73 and is reflected thereby. This reflected light is received by a detector 74. A sample 75 is oscillated by a scanner 76 mounted on a Z stage 115a. The inclination of the cantilever 73 with respect to the sample 75 on a sample holder 77 caused by the atomic force is detected as a variation in the light receiving position on the detector 74. The variation in the light receiving position is converted into a variation in the relative distance between the sample 75 and the cantilever 73.
The observation area of the AFM is determined by the oscillation range of the scanner 76 and is therefore as small as several .mu.m. Accordingly, to find a particular point on the wide sample, it is necessary to move measuring points one after another and thus, a very long time has been required for observation. Even if an attempt is made to limit the measuring points in advance by an optical microscope or the like, it has been very difficult in the prior-art AFM because of the light source 71 and the detector 74.
On the other hand, with regard to the prior-art scanning tunnel type microscope (hereinafter referred to as the STM), as shown in FIG. 13 of the accompanying drawings, there has been developed a scanning tunnel microscope of coaxial construction in which an STM scanner 116 is provided outside a visible optical system provided with the objective 112 of an optical microscope. In this microscope, a sample 117 on a Z stage 115b can first be observed by means of the image pickup device 111 of the optical microscope and the position of a probe 114 fixed to the probe holder 113 of the STM can be confirmed to thereby specify a measuring point.
Also, as shown in FIG. 14 of the accompanying drawings, there has been proposed a coaxial type scanning tunnel microscope having an STM scanner 116 disposed in a through-hole in the objective 118 of an optical microscope having a through-hole.
The AFM and STM are very similar to each other in the control method and the algorithm of observation data obtainment and therefore, as shown in FIG. 15 of the accompanying drawings, there has been developed an apparatus in which portions of the electrical control systems such as an I/V amplifier 119, a feedback circuit 120, a high voltage amplifier 121 and a display 122 are used in common. In this apparatus, only a detecting system and a driving system are changed over by switches 123 and 124, and the STM and AFM are selectively operated.
As described above, in the prior-art AFM, the observation area is several .mu.m, and to find a particular region of several .mu.m from a wide area such as an organismic sample, it has been necessary to move measuring ranges of several .mu.m one after another until the desired point of the target sample is located. This has required a very long time.
Also, in a coaxial type scanning tunnel microscope wherein the prior-art STM and an optical microscope are disposed coaxially with each other, a probe has been provided in the central portion of the optical microscope and therefore, it has been difficult in terms of space to dispose the light source of the AFM and a detector.